1. Field of the Invention
The present invention deals with the mixing of granular, particulate or pulverant material and in particular deals with methods or devices for mixing such materials by means of vibrating motion.
2. Description of the Prior Art
Various general methods and types of devices are known for the purpose of mixing two or more types of granular, particulate or pulverant materials. Such materials are commonly mixed, for example, by means of rotary movement in which material is charged into a closed mixing vessel which is then rotated about its own or some external axis. It is found, however, that such rotating motion often induces mixing in whole layers of material so that pockets of unmixed material may be found in the finished mixture. Alternatively, it is also conventional to mix such materials by means of rotating paddles. While this method often obtains a more homogenous final product than would be possible by means of a rotating closed vessel, it is found that the impacting of the rotating parts on the particles to be mixed may in some cases cause unacceptable degradation of such particles. Furthermore, the direct contact between the rotating paddles and the particles to be mixed may result in the incurrance of high costs for the purpose of maintaining and cleaning the mixing apparatus.
In view of the above described disadvantages, it has been suggested that particulate and pulverant materials be mixed by means of vibratory motion. U.S. Pat. No. 3,297,304, for example, discloses a vibratory mixer in which a stream of particulate material flows along the longitudinal axis of a vibrating trough and in which a plurality of flat inclined members are positioned at intervals along the trough's longitudinal axis. The upstream end of each of these members is in engagement with the trough bottom and the downstream end spaced above the trough bottom. Thus, the material to be mixed passes over each of the inclined members and as it is discharged it will be subject to a folding action as it falls from the elevated downstream ends of these members.
Another vibratory mixer is disclosed in U.S. Pat. No. 3,687,420. In this apparatus an inclined trough contains a mass of pulverant material, which due to the lengthwise decline of the trough moves slowly from the upper end to the lower discharge end of the trough. The entire trough is vibrated in an upward and downward direction along a path perpendicular to its longitudinal axis. Because of this vibration, the material in the trough tends to move or roll in a closed path with the material in contact with the trough moving toward and up the side of the trough and with the material on top sliding down toward the low side of the mass of material.
Although the above described vibratory mixing devices avoid problems associated with rotating or paddle mixers, they do involve the necessity of vibrating a large part, if not all, of the conveying structure. It is believed that certain efficiencies might be realized by applying vibratory motion in a more selective manner. It is, therefore, the object of the present invention to provide a method and apparatus for mixing particulate or pulverant material in which vibratory motion need only be applied at certain selected times and positions.